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Study on the chemical evolution of planetary materials and the origin of meteorites inferred from variable analyses of cosmogenic nuclides

宇宙成因核素变量分析推断行星物质化学演化和陨石起源研究

基本信息

批准号：
13440167
负责人：
HIDAKA Hiroshi
金额：
$ 8.38万
依托单位：
Hiroshima University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

项目摘要

Twelve martian meteorites, twelve aubrites (enstatite achondrites), eight fragments from the Jilin chondrite and fifteen lunar regoliths from Apollo 16 and 17 landing sites, were used in this research to study the interaction of cosmic rays with planetary materials. The samples were characterized from neutron-captured isotopic shifts of Sm and Gd, noble gasses isotopic variations, and abundances of cosmogenic isotopes such as ^<10>Be and ^<41>Ca.New findings from this research are as follows : (1) Neutron captured Sm and Gd isotopes were found in six of twelve martian meteorites. Considering little correlation between cosmic-ray exposure ages estimated from noble gas analysis and irradiated neutron fluence from Sm and Gd isotopic measurements, some of martian meteorite experienced multi-stage irradiation. This reveals a possibility of pre-irradiation of the meteorites on Mars. (2) The calculated neutron fluences for some aubrites such as Pesyanoe and Khor Temiki show significant variations even in the same meteorite, which suggests the irradiation history in the regolith of the aubritic parent body. The systematic data between neutron fluences and cosmic-ray exposure ages suggest the subdivision of aubrites into subgroups with only space irradiation and a subgroup with regolith history. (3) Lunar regolith processes can be discussed from neutron stratigraphy of the Apollo-16 and 17 drill stems. The depth profiles of neutron fluences suggest that large mixing events occurred after deposition of the regoliths and that the regoliths consists mainly of two slabs.

12块火星陨石、12块顽火辉石（顽火辉石无球粒陨石）、8块吉林陨石碎片和15块阿波罗16号和17号着陆点的月壤，被用于研究宇宙线与行星物质的相互作用。通过Sm和Gd的中子俘获同位素位移、稀有气体同位素变化以及宇宙成因同位素~（13）Be和~（13）Ca的丰度等对样品进行了表征<10><41>，得到以下新的发现：（1）在12块火星陨石中，有6块发现了Sm和Gd的中子俘获同位素。考虑到宇宙射线暴露年龄估计的惰性气体分析和辐照中子注量从Sm和Gd同位素测量之间的相关性很小，一些火星陨石经历了多阶段的照射。这揭示了火星上陨石预辐照的可能性。(2)对Pesyanoe和霍尔Temiki等陨石的中子注量率计算表明，即使在同一陨石中，中子注量率也有很大的差异，这表明了它们的母陨石风化层中的辐照历史。中子注量率和宇宙射线暴露年龄之间的系统数据表明，Aubrites细分为亚组，只有空间照射和一个亚组的风化历史。(3)从阿波罗16号和17号钻柱的中子地层学可以讨论月球风化过程。中子注量的深度剖面表明，大的混合事件发生后沉积的风化层和风化层主要由两个板。